Portland's weather is pleasant today: crisp and cold. Wednesday, however, was damp and gray—and smoky.

That's because smoke from northern California's Camp Fire—one of the worst blazes in the state's history—has begun to drift into the Portland area.

According to the Oregon Department of Environmental Quality's air quality data, conditions in Portland are currently rated unhealthy for sensitive groups. That means children and older adults and people with lung or heart conditions should avoid outdoor activity.

In an air quality advisory issued by DEQ this morning, the agency notes that warnings are in effect for much of Oregon as well as Southwest Washington.

Laura Gleim, an Oregon DEQ spokesperson, says that Portland's air quality readings have been fluctuating the past couple days, and that the agency tends to "issue an advisory when [smoke] stagnation persists for several days."

Gleim adds that air quality is worse in the evenings "when weather stagnates and things settle."

Multnomah County is also one of five Oregon counties to issue wood burning restrictions, limiting the use of fireplaces, outdoor fire pits and wood stoves.

Gleim says adhering to the burn restriction is one thing residents "can to do help their neighbors."

The National Weather Service predicts the air quality advisory could be in effect until Friday evening.

"Smoke might hold through tonight and tomorrow," Gleim says, "but if wind picks up then it could clear out quicker. Or it could go other way and get worse."

The Camp Fire, which has been burning since Nov. 8 and reportedly was sparked by a down Pacific Gas & Electric Co. power line, has killed 59 people and leveled 9,000 homes. 130 people are still reported missing.

Further south, the Woolsey Fire has also ripped through the towns of Malibu and Agoura Hills, destroying around 500 homes and killing three people.

This isn't the first time this year Portland has been plagued by wildfire smoke. In August, haze from west coast wildfires drifting into the city briefly place Portland at number one for worst air quality in any major North American city.